This invention relates to a radio frequency identification tag (RFID tag) for transmitting the information recorded in an IC chip by radio communication, or in particular to a “RFID tag” mounted on the surface of a metal sheet and a “RFID tag” manufacturing method.
In recent years, a “RFID tag” has come to find wide applications for information control of articles and structures or distribution control. The “RFID tag” is configured of a small IC chip having recorded information therein and a small antenna for transmitting the information in the IC chip by radio communication. The “RFID tag” is used by being attached to an article or buried in a structure. The IC chip is as small as about 0.4 mm×0.4 mm size by 0.1 mm high. By bringing a reader-writer in proximity to this “RFID tag”, the information (i.e. the information on the attributes of individual articles and structures) recorded in the IC chip can be read without contact. Considering the manufacturing cost and the mounting ease, the “RFID tag” is preferably as small and lightweight as possible.
A “RFID tag” is available, for example, in which on a first antenna connected to an IC chip, a second antenna (auxiliary antenna) is arranged through a second spacer of a dielectric material, and by increasing the radio intensity utilizing the amplification due to the resonance of the second antenna, the communication distance can be increased even in the presence of considerable amount of metal or moisture. Also, a technique is known in which a slot antenna is formed on the surface of a metal plate and brought into contact with a terminal of the IC chip as a metal, thereby achieving superior antenna characteristics even on the surface of a metal plate (JP-A-2002-358494, Paragraphs 0009 to 0018 and FIGS. 1 to 3).
In recent years, application of the “RFID tag” to information control of medicine in such forms as tablets and capsules has been desired as well as general articles or structures. The medicines in the form of tablets and capsules are sealed in PTP (Press Through Package) which is a kind of heat sealed package. One surface of the package is covered entirely by a resin sheet such as PVC in the thickness of 0.2 to 0.25 mm, and the other surface is entirely covered by an aluminum sheet. The aluminum sheet reduces the communication distance, and therefore the ordinary “RFID tag” cannot be used, a “RFID tag” compatible with a metal is required. The use of a “RFID tag” suitable for a metal, however, would increase the size and cost of the package and therefore not suitable for packaging medicines in general.